Finding Cryptic Insect Eggs With Fluorescence

I recently gave a talk on some of my work as a PhD student on experiments manipulating densities of the tea green leafhopper (Empoasca onukii) on tea plants. What the audience liked most, I think, were my methods for finding leafhopper eggs in the field and rearing them in the lab (well, a guest room at a tea farm). You see, leafhoppers (including at least the tea green leafhopper and the small green leafhopper, Empoasca vitis) lay their eggs inside plant tissues, making them impossible to find with the naked eye. But, you can take advantage of the fluorescent properties of leafhopper eggs and plants to make them more visible.

Students from TRI CAAS looking for leafhopper eggs in tea shoots

Figure 1: Students from TRI CAAS looking for leafhopper eggs in tea shoots

It turns out that under blue light, leafhopper eggs fluoresce bright green while the chlorophyll in plants fluoresces red. By using blue light to create this fluorescence and blocking the blue light coming to your eyes with a filter, you can easily spot the eggs even though they are under the epidermis of the tea stems.

What you’re seeing above is video from a smart phone with the lens covered by a pair of orange goggles. I move the beam of a blue LED flashlight (which you can’t really see because of the orange filter) toward the center of the frame, where you see a green dot appear on the tea stem. This is a leafhopper egg. Then I remove the orange goggles so you can see what it looks like without them—totally washed out by blue light.

A tea shoot lit by ambient light (left) and by blue light, filtered through orange goggles (right).  The leafhopper egg is the small green dot on the stem in the right panel.

Figure 2: A tea shoot lit by ambient light (left) and by blue light, filtered through orange goggles (right). The leafhopper egg is the small green dot on the stem in the right panel.

This method is modified from a 2004 paper by Herrmann and Böll that was written before bright blue LEDs were widely available, and calls for the use of full-spectrum white light from a halogen bulb passed through a filter. Now, blue LED flashlights are cheap and widely available, providing a much more portable solution for field sampling. I used a small blue flashlight I bought from Amazon for my light source, and some orange, UV-blocking goggles for my blue light filter, but any blue light source and orange goggles should work! I should also mention, that this is best done at dusk or nighttime to improve visibility.

Whether you’re working in a vineyard to monitor Empoasca vitis, trying to rear leafhoppers from eggs, or trying to count eggs in an oviposition choice experiment, using this method will save you time and frustration.

Acknowledgements:

Guan-Hua Liu and Long Jiao helped to confirm that the eggs I was finding were Empoasca onukii eggs. Thanks guys!

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